Many drugs are provided in aqueous solution. For this purpose, they are typically packaged, in a glass, plastics or other container such as an ampoule, vial or bag, and sterilised by autoclaving. They can then be stored and used as necessary.
One class of drugs that is administered as a solution, e.g. by injection or infusion, comprises the long-acting local anesthetics which include an amine. Particular examples of this type of therapeutic agent are 1-alkyl-N-(2,6-dimethylphenyl)-2-piperidinecarboxamides, of which specific examples are mepivacaine, ropivacaine, bupivacaine and levobupivacaine. These drugs are usually provided as the hydrochloride salt.
Jones et al, Am. J. Hosp. Path. 50(11):2364-5 (1993), reports that there were no significant changes in assay or pH upon storage of bupivacaine in polypropylene syringes.
Similarly, Upton etat, Aus. J. Hosp. Pharm. 17(4): 267-70 (1987), demonstrated no adsorption of bupivacaine to a range of plastics inducing polypropylene.
Hampe Da Poian et al, Revista Brasileira de Anestesiologia 33(1):23-5 (1983), reported no significant changes in pH or stability of solutions of bupivacaine (0.25%, 0.5%, 0.75%) following sterilisation in glass ampoules.
Chem. Abs. 97(25):222883 (1982) indicates that solutions of bupivacaine in vials were stable to heat and light following sterilisation.
U.S. Pat. No. 5,505,922 discloses a combination of a local anesthetic and lithium ions, to provide enhanced anesthetic activity. The lithium ions are described as a buffer. Among various possible additional components, it is suggested that pH buffers may be used to establish a physiologically compatible pH range and to enhance the solubility of the anesthetic.